Antenna system



- Nov. {5, 1946 GJH. BROWN EI'AL ANTENNA SYSTEM 2 shts-sneet 1 Filed Oct. 31 1944 gawk Darluld Mfriersam Mme/WY Nvzw 5, 1946 a; H. BRQWN ETA], 2,191,597 ANTENNA SYSTEM Filed Oct. 31, 1944 2 Sheets-Sheet 2 Patented Nov. 5, 1946 PATENT OFFICE 2,410,597 ANTENNA SYSTEM George H. Brown and Donald W. PetersomPrinceton, N. J assignors to Radio Corporation of America, a corporation of Delaware Application October 31, 1944, Serial N 0. 561,189

11 Claims.

Thi invention relates to antenna systems, and more particularly to improved directive antenna systems providing directive patterns in the form of relatively narrow beams, and operative over broad frequency bands with high efiiciency.

. 2 along the line of the centers of the radiators l, 3, 5, and 1. See Figure 3.

The principal object of the present invention is to provide an improved broad band antenna system of the type including a plurality of spaced directivity with minimum Works may be designed so that the overall system maintains a relatively constant throughout a broad frequency band.

A further object is to provide an improved system of the described type which may be deimpedance signed to employ coaxial transmission lines of standard commercially available impedances.

These and other objects will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawings, wherein:

Figure l is a schematic plan view of an antenna system constructed in accordance with the invention,

Figure 2 illustrates schematically the construction of a preferred type of radiator element for use in the system of Figure 1,

Figure 3 is a sectional view of a reflector included in the system of Figure 1,

Figure 4 is a longitudinal section of a combined line balance convertor and power division device employed in the system of Figure 1,

Figure 5 is a cross section of the device of Figure 4 along the line V-V,

Figure 6 is a graph illustrating the standing wave ratio as a function of frequency on a feed line connected to the system of Figure 1, and

Figure 7 is a graph illustrating the horizontal beam width provided by the system of Figure l, as a function of frequency.

The invention will be described as embodied in a'system of the type illustrated in Figure 1, which include a generally conventional arrangement of four radiator groups I 3, 5 and 1 disposed in a line substantially perpendicular to the axis of the desired directive pattern. Vertical directivity is provided by means of a reflector 9 of conductive material in the form of a cylindrical paraboloid with its focal line disposed The radiator groups I, 3, 5 and 7 are spaced at equal intervals along the focal line of the reflector 9. The directive pattern of such an array (i. e. four radiators, equally spaced, in line) can be predicted in accordance with known engineering principles. It is found that high directivity, in view of the number of radiators, and

minimum secondary lobes in the directive pattern, will be obtained by exciting the outer groups I and l each with 10 percent of the available power input, and the inner groups 3 and 5 each with 40 percent of the available input.

The necessary division of power between the various radiators has been effected heretofore by various means, practically all of which will operate efiiciently only at the single frequency for which they are designed, owing to the use of resonant elements such as matching and phasing stubs in the networks. In accordance with the present invention, power. division is accomplished by networks of the line balance convertor type, such as that described in copending U. S. application Ser. No. 550,566 filed August 22, 1944, by G. H. Brown and D. W. Peterson and entitled Radio power division networks. Such networks operate efiiciently throughout an extremely wide band of frequencies.

In order to secure the degree of horizontal directivity required in certain applications, it is necessary that each of the radiator groups I, 3, 5 and I comprise three spaced radiators, excited in phase. In the system of Figure 1, each of the radiator groups comprises three dipoles ll, 13 and I5 disposed in end-to-end relationship and spacedat equal intervals. .To provide the required cophasal relationships, the dipoles of each group are connected in parallel with each other by means of transmission lines [6 extending to junction points I! and IS. The lines l6 preferably comprise coaxial cables. Two cables are required for each dipole; one for each radiator element. The inner conductors only of the lines it are shown in Figure 1. The outer conductors are all connected together and grounded. To provide excitation of the dipoles, current must flow into one of the radiator elements while current is flowing out of the other element. Thus each pair of the lines I6 functions as one conductor of a parallel conductor transmission line, and the points ll and I9 must be of opposite polarity.

The junction points l1 and H! are the output terminals of a line balance convertor 2|, illusaiida'i trated in detail in Figure 4. The convertor 2i has an unsymmetrical input circuit (that is, one side i grounded) connected to a coaxial line 23. The convertor 2! couples the unsymmetrical circult of the line 23 to the symmetrical circuits of the lines l6.

Refer to Figure 4. The convertor 2i comprises a conductive sleeve l25 surrounding the final quarter wave section of the line 23 and connected to the outer conductor thereof by means of a disc member I21. The sleeve 125 is one-half wavelength long at the center of the band of frequencies throughout which the system is to operate. The outer end of the sleeve 125 is connected by means of a disc 129 to a coaxial tubular conductor i3i, approximately one-quarter wavelength long and of a diameter substantially equal to that of the outer conductor of the line 23. The inner end of the member IN is connected to the end of the inner conductor of the line 23. The inner end of the conductor i3! is the junction point IT, and the end of the outer conductor of the line 23 is the junction point is. The outer conductors of the lines It are connected to the sleeve [25.

In operation, the member l3l cooperates with the sleeve I25 to function as a quarter wave line short-circuited at one end. Similarly, the outer conductor of the line 23 cooperates with the sleeve 125 to function as a second quarter wave line short-circuit'ed at the other end. Current flowing in on the inner conductor of the line 23 fiows down the member 'l-3l to the disc I29, thence through the sleeve I25 to the outer conductor of the line 23, and along the outer surface of the outer conductor of the line 23 in the same direction as the current on the conductor 13L Thus the junction points ll and I9 are symmetrical with respect to ground; and current is flowing into one while current flows out of the other, fulfilling the requirement for symmetrical excitation of the dipoles connected to the lines l6.

It should be noted that the coupling of the line it to the line 23 is substantially equivalent to a series parallel connection. Thatis, if each of the lines It has a characteristic impedance of 75 ohms, and is matched at its load end, the impedance presented to the line 23 is or 50 ohms. In an antenna system of the described type it is highly desirable to employ coaxial lines of standard commercially obtainable characteristics. 50 ohms and 75 ohms are both standard impedances. '75 ohm cables may be used for lines Iaand 50 *ohm'cables for the lines 23.

The conventional dipole structure exhibits a relatively low impedance, particularly if designed in accordance with conventional practice to provide broad band operation. However, structures of the type illustrated in Figure 2 and described and claimed in copending U. S. application Ser. No. 552,095, filed August 31, 1944, by D. W. Peterson and entitled Broad band radiator, may be designed to provide an impedance which remains relatively constant at a value of'the order of '70 ohms over a broad band of frequencies. If such elements are used in the dipoles H, i3 and t5, the lines It will remain substantially matched throughout theoperating range.

Referring to Figure 2, a typical dipole structure of the above-mentioned type comprises a pair of cylindrical members 25, disposed in endto-end relationship and each provided with a plurality of transverse radial fins 21. The dimensions and spacings of the fins may be adjusted to provide the required impedance characteristics.

The input ends of the lines 23 are connected to a power dividing network 29 which may be of the type described in the above-mentioned Brown and Peterson application Ser. No. 550,566. The device 29 includes a coaxial line section 3! onehalf wavelength long at the center of the band of operation, connected at one end to a line balance converter 33 and at the other end to the main feed line 35 and to a quarter wave short circuited stub 31. The convertor 33 comprises a quarter-wave sleeve 39 surrounding the final quarter-wave-section of one of the lines 23 and connected thereto by a disc H. Another of the lines 23 has its outer conductor connected at the point 43 tothe sleeve 39 and its inner conductor connected to the first of the lines 23-. The two lines 23 thus far mentioned are connected respectively to the radiator groups I and 7, which are thus connected in series with each other through the convertor 33. 'Since current is flowing into one of these lines while current is flowing out of the other, the connections to the dipoles of thegroup i must be reversed with respect to those of the group I in order that groups 5 and I shall operate in phase. The remaining pair of lines 23 extending to the radiator groups 3 and 5 are connected in parallel to each other to the line 3!. The characteristic impedance of the section 3! is determined in accordance with the impedances of the lines 23 as described in detail in said Brown and Peterson application, for cooperation with the stub 31 to provide substantial compensation of the re'actance of the converter 33. Since the lines extending to the radiator groups 3 and 5 are in parallel to each other across the input circuit, and those extending to. the groups 1 and l are in series with each other across theinput circuit, '10 percent of the input power will flow to each of the groups I and l and ii) percent will flow to each of the groups 3 and 5.

The impedance looking into the line 35 is approximately 20 ohms. This may be matched to a ohm line by means of a coaxial transformer comprising a series of quarter-wave line sections of consecutively increasing characteristic impedances. This type of transformer, which is described and. claimed in U. S. Patent 2,249.59'1, will operate over a wide band of frequencies without variations in performance such as result from the use of matching stubs.

The graph of Figure 6 illustrates the variation with frequency of the standing wave ratio appearing on the input line "35. This gives an indication of the variations of impedance of the systein 'withfrequency. The curve of Figure '7 is the result of measurements made upon asystem like that shown in Figure 1, designed for operation over the frequency band of approximately 400 to 900 megacycles per second.

The graph of Figure 7 illustrates the variation with frequency of the horizontal width at half held of the beam provided by the system of Figure 1. The beam becomes narrower as the frequency is increased, owing to the fact that the various dimensions 'of the system become increasingly larger in relation to the wavelength.

Briefly summarizing the above description, the invention comprises an'improved broad band directive antenna system wherein high impedance dipoles are employed to enable the use of coaxial wide band of frequencies. between the radiator elements of each radiator transmission lines of standard impedances, and a power division network of the line balance convertor type is used to enable accurate power division and eficient power transfer throughout a Power is subdivided group by means of a combined balance converter and power division device which also operates with high efficiency throughout the required frequency band. Although the invention has been described as embodied in an antenna including four radiator groups, it will be apparent to those skilled in the art that the principles disclosed herein may be applied with similar advantage to antennas comprising larger numbers of radiator groups, in which structures like that of Figure 1 are used as subcombinations.

The invention covered herein may be manufactured and used by or for the Government of the United States for any governmental purpose without payment to me or assigns of any royalty thereon.

We claim as our invention:

1. A broad band directive antenna system, including four groups of collinearly disposed radiator elements, constituting two side groups and two center groups, four coaxial transmission lines, one coupled to each of said groups respectively, a main feed line, means for coupling said coaxial lines associated with said side groups in series with each other across said main feed line, and means for coupling said coaxial lines associated with said center groups in parallel with each other across said main feed line.

2. A broad band directive antenna system, including four groups of radiator elements constituting two side groups and two center groups, each of said groups comprising a plurality of collinear dipoles, four coaxial transmission lines extending respectively to said radiator groups, line balance convertor means connected to the dipoles of each group and to the respective transmission line so as to couple all of the dipoles of each group in parallel with each other to the respective line, a main feed line, means for coupling said coaxial lines associated with said side groups in series with each other to said main feed line, and

means for coupling said coaxial lines associated with said center groups in parallel with each other to said main feed line.

3. A broad band directive antenna system, including a reflector in the form of a cylindrical paraboloid, four groups of radiator elements disposed in line along the focal line of said reflector,

each of said groups comprising a plurality of collinear dipoles, four coaxial transmission lines extending respectively to said radiator groups, line balance converter means connected to each group and to the corresponding transmission line so as to couple all of the dipoles of each group in parallel with each other to the respective line, a main feed line, means for coupling said coaxial lines associated with the outer pair of said groups in series with each other to said main feed line, and means for coupling said coaxial lines associated with the inner pair of said groups in paral lel with each other to said main feed line.

4. A broad band directive antenna system, including a reflector in the form of a cylindrical paraboloid, four groups of radiator elements disposed in line along the focal line of said reflector, each of said groups comprising three collinear dipoles, four coaxial transmission lines extending respectively to said radiator groups, line balance convertor means connected to each group and to th corresponding transmission line so as to cou ple all of the dipoles of each group in parallel with each other to the respective line, a main feed line, means for coupling said coaxial; lines associated with the outer pair of said groups in series with each other to said main feed line, and means for coupling said coaxial lines, associated with the inner pair of said groups in parallel with each other to said main feed line.

5. A broad band directive antenna system, including a reflector in the form of a cylindrical paraboloid, four groups of radiator elements disposed in line along the focal line of said reflector, each of said groups comprising a plurality of collinear dipoles, four transmission lines extending respectively to said radiator groups, means for coupling all of the dipoles of each group in parallel with each other to the respective line, a main feed line, means for coupling said linesv associated with the outer pair of said groups inseries with each other to said main feed line, and means for couplingsaid lines associated with, the inner pair of said groups in parallel with each other to said main feed line.

6. A broad band directive antenna system, including a reflector in the form of a cylindrical paraboloid, four groups of radiator elements disposed in line along the focal line of saidrefiector, each of said groups comprising a plurality of collinear dipoles, each dipole comprising a pair of tubular conductors provided with a plurality of conductive fins lying in planes at right angles to the axis of said conductors, four coaxial transmission lines extending respectively to said radiator groups, line balance converter means connected to each group and to the corresponding transmission line so as to couple all of the dipoles of each group in parallel with each other to the respective line, a main feed line, means for coupling said coaxial lines associated with the outer pair of said groups in series with each other to said main feed line, and means for coupling said coaxial lines associated with the inner pair of said groups in parallel with each other to said main feed line.

'7. A broad band directive antenna system, including a reflector in the form of a cylindrical paraboloid, four groups of radiator elements disposed in line along the focal line of said reflector, each of said groups comprising three dipoles, each dipole comprising a pair of tubular conductors provided with a plurality of conductive fins lying in planes at right angles to the axis of said conductors, four coaxial transmission lines extending respectively to said radiator groups, line balance convertor means connected to each group and to the corresponding transmission line so as to couple all of the dipoles of each group in parallel with each other to the respective line, a main feed line, means for coupling said coaxial lines associated with the outer pair of said groups in series with each other to said main feed line, and means for coupling said coaxial lines associated with the inner pair of said groups in parallel with each other to said main feed line.

8. A broad band directive antenna system, including a reflector in the form of a cylindrical paraboloid, four groups of radiator elements disposed in line along the focal line of said reflector, each of said groups comprising a plurality of collinear dipoles, each dipole comprising a pair of tubular conductors provided with a plurality of conductive fins lying in planes at right angles to the axis of said conductors, four transmission lines extending respectively to said radiator with the inner pair of said groups in parallel with 4 each other to said main feed line.

9. A broad band directive antenna system, including a reflector, four groups of radiator elements disposed in cooperative relationship with said reflector, each of said groups comprising a plurality of dipoles, four coaxial transmission lines extending respectively to said radiator groups, line balance convertor means connected to each group and to the corresponding transmission line so as to couple all of the dipoles of each group in parallel with each other to the respective line, a main feed linemeans for coupling said coaxial lines associated with one pair of said groups in series with each other to said main feed line, and means for coupling said coaxial lines associated with the other pair of said groups in parallel with each other to said main feed line.

10. A broad band directive antenna; including a plurality of spaced groups of radiator elements disposed in pairs symmetrically about a central line, transmission lines extending respectively to said radiator groups, a main feed line, and line balance converter means for coupling said lines associated with certain pairs of said groups in series with each other to said main feed line, and for coupling said lines associated with the remainder of said groups in parallel with each other to said main feed line.

11. A broad band directive antenna, including a plurality of spaced groups of radiator elements disposed in pairs symmetrically about a central line, each of said groups comprising a plurality of collinear dipoles, each dipole comprising apair of tubular conductors provided with a plurality of conductive fins lying in planes at right angles to the axis of said conductors, transmission lines extending respectively to said radiator groups, line balance converter means connected to each group and to the corresponding transmission line so as to couple all of the dipoles of each group in parallel with each other to the respective line, a main feed line, and line balance converter means for coupling said lines associated with certain pairs of said groups in series with each other to said main feed line, and for coupling said lines associated with the remainder of said groups in parallel with each other to said main feed line.

' GEORGE H. BROWN.

DONALD W. PETERSON. 

